Selective call radio receivers such as pagers alert a user when a received signal includes an address code signal identifying that particular selective call receiver. Such devices generally incorporate a radio receiver capable of producing, for example, either an audible alert which may be heard by the user or a tactile alert such as a vibrating sensation which may be felt by the user. Some pagers provide the additional features of a voice message or a message visually displayed on a screen.
Each selective call receiver is identified by a specific address that typically precedes each message. When a selective call receiver receives a message preceded by that selective call receiver's address, the message is stored within a memory for subsequent presentation.
The theft of selective call receivers has become a problem in the industry, especially for the system operators that store large quantities of selective call receivers in warehouses. Due to the signaling format standardization for transmitting the address and message, the selective call receivers are readily interchangeable by modifying a stolen selective call receiver for operation on a different system. When two paging systems operate with the same coding format, it is only necessary to change the operating frequency and the address word of the selective call receiver. It is extremely easy to change the address word commonly contained in a readily modifiable EEPROM code plug, and since most carrier based selective call systems in the United States operate on less than ten frequencies, it is relatively easy for an electronic technician to change the radio frequency of the selective call receiver.
As the design of selective call receivers evolves toward the use of frequency synthesizers and decoders that can decode several different code formats, the theft and conversion of selective call receivers will become even easier in that the conversion process will only involve changing the information contained in an EEPROM.
Thus, what is needed is a selective call receiver that's use is limited to one transmitting system, or to multiple systems with a common operator or owner.